From Paul Dietz
The hypothetical halo planets present an interesting possibility for directly benefiting mankind (23 July, p 28). A Mars-sized or larger planet in the outer solar system should be able to retain an atmosphere containing helium, including the promising fusion fuel helium-3. It may be easier to mine He-3 there than from other sources, such as lunar regolith or the atmospheres of the gas giants. Reasonable travel times to the halo planets would require use of a fusion rocket with high specific impulse – but if we’re mining He-3 we presumable already have working fusion reactors.
Lake in the Hills, Illinois, US
